One of the most remarkable features of the nervous system is its capacity to undergo experience- dependent rewiring. Synaptic plasticity, the change in the number and efficacy of synaptic connections with experience, provides the basis for memory formation and storage in the brain. Long-lasting plasticity, such as that underlying long-term memory, requires new gene expression. Investigating how synaptically generated signals are transported from stimulated synapses to the nucleus to regulate transcription, the Martin lab previously uncovered a role for the synapse to nuclear transport of the transcriptional regulator CRTC1 (Ch'ng et al. 2012), a co-activator and regulator of CREB-dependent transcription. CRTC1 activity is regulated by desphosphorylation, with phosphorylated CRTC1 being cytoplasmically localized and dephosphorylated CRTC1 localizing to the nucleus. Thus, CRTC1 is anchored at synapses in unstimulated neurons, but undergoes rapid translocation to the nucleus in response to glutamatergic stimulation. In the nucleus, CRTC1 regulates the expression of CREB target genes. A striking finding that emerged from our studies was that CRTC1 underwent dramatic and complex changes in phosphorylation following neuronal stimulation. Initial mass spectrometric analyses revealed 50 amino acid residues in CRTC1 that are phosphorylated in the neuroblastoma N2a cell line. My fellowship research project aims to map the residues that undergo regulated dephosphorylation during long-term plasticity in mouse hippocampal neurons. As models of plasticity, I will study long-term potentiation (LTP) and long-term depression (LTD) of acute mouse hippocampal slices. My experiments test the hypothesis that distinct patterns of activity trigger distinct changes in the pattern of CRTC1 phosphorylation and that the differentially phosphorylated forms of CRTC1 regulate distinct programs of gene expression. In this way, the post-translational modification of CRTC1 can encode patterns of stimulation to produce appropriate changes in gene expression. To test this hypothesis, I propose two aims. In the first, I determine how LTP and LTD inducing stimuli alter the phosphorylation of CRTC1. In the second, I determine how these stimuli regulate the interaction of CRTC1 with specific transcription factors and how these complexes regulate downstream gene expression.